Liquid jet apparatus and printing apparatus

ABSTRACT

A liquid jet apparatus according to the present invention is a liquid jet apparatus including a plurality of nozzles, an actuator provided for each nozzle and connected to the respective nozzle, a drive waveform signal generation unit that generates a drive pulse, and a drive unit that applies the drive pulse to the actuator, wherein the drive unit includes a transistor pair, wherein the transistor pair: has two transistors connected to each other in a push-pull manner, and power-amplifies the drive pulse. The drive unit also includes a low-pass filter disposed between the transistor pair and the actuator.

This application is a divisional of Ser. No. 11/780,390 filed Jul. 19,2007 which is incorporated by reference and claimed priority to Japaneseapplication no. 2006-200353 filed Jul. 24, 2006 and Japanese applicationno. 2007-184439 filed Jul. 13, 2007.

BACKGROUND

1. Technical Field

The present invention relates to a liquid jet apparatus and printingapparatus arranged to print predetermined letters and images by emittingmicroscopic droplets of liquids from a plurality of nozzles to form themicroscopic particles (dots) thereof on a printing medium.

2. Related Art

An inkjet printer as one of such printing apparatuses, which isgenerally low-price and easily provides high quality color prints, haswidely spread not only to offices but also to general users along withthe widespread of personal computers and digital cameras.

In recent inkjet printers, printing in fine tone is required. Tonedenotes a state of density of each color included in a pixel expressedby a liquid dot, the size of the dot corresponding to the color densityof each pixel is called a tone grade, and the number of the tone gradescapable of being expressed by a liquid dot is called a tone number. Finetone denotes that the tone number is large. In order to change the tonegrade, it is required to modify a drive pulse to an actuator provided toa liquid jet head. In the case in which a piezoelectric element is usedas the actuator, since the amount of displacement of the piezoelectricelement (distortion of a diaphragm, to be precise) becomes large whenthe voltage value applied to the piezoelectric element becomes large,the tone grade of the liquid dot can be changed very accurately.

Therefore, in JP-A-2003-1824, a plurality of drive pulses with differentwave heights are combined and joined, the drive pulses are commonlyoutput to the piezoelectric elements of the nozzles of the same colorprovided to the liquid jet head, a drive pulse corresponding to the tonegrade of the liquid dot to be formed is selected for every nozzle out ofthe plurality of drive pulses, the selected drive pulses are supplied tothe piezoelectric elements of the corresponding nozzles to emit dropletsof the liquid different in amount, thereby achieving the required tonegrade of the liquid dot.

However, there is a problem that the waveform of the drive pulse isdistorted by the parasitic inductance, the parasitic capacitance, andthe resistance of the wiring of the drive circuit, and the capacitanceof the actuator, such as a piezoelectric element, and moreover, theamount of the waveform distortion varies in accordance with the numberof actuators, such as piezoelectric elements, driven by the drive pulse.The waveform distortion of the drive pulse leads to variation in theamount of the liquid, causing variation in the size of the liquid dot,thus leading to degradation of the print quality. It should be notedthat the variation in the amount of the liquid also depends on theindividual difference of the nozzle or the actuator. Further, in thecase in which a plurality of drive pulses is combined in chronologicalorder and joined to each other, the drive pulse corresponding to thetone grade of a liquid dot to be formed is selected for every nozzlefrom the plurality of drive pulses, and the selected drive pulse isapplied to the actuator of the corresponding nozzle, there is caused ashift in the liquid jet emission timing between the nozzles of theactuators for which the different drive pulses are selected, thus theliquid dot forming (or landing) positions vary and cause degradation ofthe print quality.

BRIEF SUMMARY OF THE INVENTION

The present invention includes a liquid jet apparatus and a printingapparatus capable of preventing waveform distortion of the drive pulse,suppressing and preventing the variation in the amount of liquid jetted,and preventing the shift in liquid jet emission timing, therebyachieving high-quality, fine tone, printing.

A liquid jet apparatus according to the present invention is a liquidjet apparatus including a plurality of nozzles, an actuator provided foreach nozzle and connected to the respective nozzle, a drive waveformsignal generation unit that generates a drive pulse, and a drive unitthat applies the drive pulse to the actuator, wherein the drive unitincludes a transistor pair, wherein the transistor pair: has twotransistors connected to each other in a push-pull manner, andpower-amplifies the drive pulse. The drive unit also includes a low-passfilter disposed between the transistor pair and the actuator.

According to the liquid jet apparatus of the invention described above,since only one actuator is connected to the drive unit composed of thetransistor pair and the low-pass filter, waveform distortion of thedrive pulse can be prevented, therefore, variation in the amount ofliquid to be emitted can be suppressed and prevented making it possibleto perform high quality, fine tone, printing.

Further, it is preferable that the drive unit includes a modulator unitprovided for pulse-modulating the drive pulse to produce a modulatedsignal, and a gate drive unit driving the transistor pair in accordancewith the modulated signal.

Further, it is preferable that the liquid jet apparatus includes awaveform data memory for storing waveform data corresponding to theactuators, wherein the drive waveform signal generation unit generatesthe drive pulse for each actuator in accordance with the correspondingwaveform data stored in the waveform data memory.

According to the liquid jet apparatus of the invention described above,by generating the drive waveform signal corresponding to the actuator ofthe individual drive circuit and the nozzle, the variation in the amountof liquid to be emitted among the nozzles can be suppressed andprevented, thus high quality, fine tone, printing becomes possible.

Further, it is preferable that the drive waveform signal generation unitgenerates the drive waveform signals simultaneously with the timing ofemitting the liquid jet from the nozzles to all of the actuatorscorresponding to the nozzles from which the liquid jet is to be emitted.

According to the liquid jet apparatus of the invention described above,the shift of the liquid jet emission timing among the nozzles can beprevented, thus high quality, fine tone, printing becomes possible.

Further, it is preferable that the drive unit is disposed adjacent tothe actuators as an integrated circuit.

Further, the printing apparatus of the invention is preferably aprinting apparatus provided with the liquid jet apparatus describedabove.

According to the printing apparatus of the invention described above,the variation in the amount of liquid to be emitted can be suppressedand prevented, thus high quality, fine tone, printing becomes possible.Further, by disposing the drive unit adjacent to the actuators as anintegrated circuit, power loss can be reduced to achieve low powerconsumption, and at the same time, the plurality of liquid jet heads canefficiently be arranged, thus reducing the size of the printingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a top view of an overall configuration showing anembodiment of a line head printing apparatus applying the liquid jetapparatus according to the present invention;

FIG. 1B is a front view of the line head ink jet printer of FIG. 1A;

FIG. 2 is a block diagram of a control device of the printing apparatusshown in FIG. 1;

FIG. 3 is an explanatory diagram of generation of the drive waveformsignal;

FIG. 4 is an explanatory diagram of the drive waveform signals invarious forms;

FIG. 5 is a block diagram of the drive circuit as a unit;

FIG. 6 is a block diagram showing the overall configuration of the drivecircuit;

FIG. 7 is a block diagram showing details of the modulator, the digitalpower amplifier, and the low-pass filter of the drive circuit shown inFIG. 5;

FIG. 8 is an explanatory diagram of the operation of the modulator shownin FIG. 7;

FIG. 9 is an explanatory diagram of the operation of the digital poweramplifier shown in FIG. 8;

FIG. 10 is a block diagram of a drive waveform generator;

FIGS. 11A and 11B are explanatory diagrams of a waveform data memory;

FIG. 12 is a flowchart showing an arithmetic process of waveform dataoutput performed by the memory controller shown in FIG. 10; and

FIG. 13 is an explanatory diagram of a drive waveform signal by thearithmetic process shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment will be explained with reference to the drawings, using aprinting apparatus for printing letters and images on a print medium byemitting a liquid, as an example of the present invention.

FIGS. 1A and 1B are schematic configuration views of the printingapparatus according to the present embodiment, wherein FIG. 1A is a topplain view thereof, and FIG. 1B is a front view thereof. In FIG. 1, inthe line head printing apparatus, a print medium 1 is conveyed from theupper right to the lower left of the drawing along the arrow direction,and printing occurs in a print area in the middle of the conveying path.It should be noted that the liquid jet heads of the present embodimentare not arranged in one line, but are arranged in two lines.

A first line of liquid jet heads 2 are arranged on the “upstream” sidein the direction of conveyance of the print medium 1. A second line ofliquid jet heads 3 are arranged on the downstream side. A firstconveying section 4 for conveying the print medium 1 is disposed belowthe first liquid jet head 2, and a second conveying section 5 isdisposed below the second liquid jet head 3. The first conveying section4 is composed of four first conveying belts 6 disposed withpredetermined intervals in the direction (hereinafter also referred toas a nozzle array direction) traversing the conveying direction of theprint medium 1, the second conveying section 5 is similarly composed offour second conveying belts 7 disposed with predetermined intervals inthe nozzle array direction.

The four first conveying belts 6 and the similar four second conveyingbelts 7 are alternated with respect to each other. In the presentembodiment, out of the conveying belts 6 and 7, the two first and secondconveying belts 6 and 7 in the right side in the nozzle array directionare distinguished from the two first and second conveying belts 6 and 7in the left side in the nozzle array direction. In other words, anoverlapping portion of two of the first and second conveying belts 6 and7 in the right side in the nozzle array direction is provided with aright side drive roller 8R, an overlapping portion of two of the firstand second conveying belts 6 and 7 in the left side in the nozzle arraydirection is provided with a left side drive roller 8L, a right sidefirst driven roller 9R and left side first driven roller 9L are disposedon the upstream side thereof, and a right side second driven roller 10Rand left side second driven roller 10L are disposed on the downstreamside thereof. Although these rollers may appear to be single rollers,they are actually decoupled in the center portion of FIG. 1A.

Further, the two first conveying belts 6 in the right side in the nozzlearray direction are wound around the right side drive roller 8R and theright side first driven roller 9R, the two first conveying belts 6 inthe left side in the nozzle array direction are wound around the leftside drive roller 8L and the left side first driven roller 9L, the twosecond conveying belts 7 in the right side in the nozzle array directionare wound around the right side drive roller 8R and the right sidesecond driven roller 10R, and the two second conveying belts 7 in theleft side in the nozzle array direction are wound around the left sidedrive roller 8L and the left side second driven roller 10L. Further, aright side electric motor 11R is connected to the right side driveroller 8R, and a left side electric motor 11L is connected to the leftside drive roller 8L. Therefore, when the right side electric motor 11Rdrives the right side drive roller 8R, the first conveying section 4composed of the two first conveying belts 6 in the right side in thenozzle array direction and similarly the second conveying section 5composed of the two second conveying belts 7 in the right side in thenozzle array direction move in sync with each other and at the samespeed when the left side electric motor 11L drives the left side driveroller 8L, the first conveying section 4 composed of the two firstconveying belts 6 in the left side in the nozzle array direction andsimilarly the second conveying section 5 composed of the two secondconveying belts 7 in the left side in the nozzle array direction move insync with each other and at the same speed.

It should be noted that by arranging the rotational speeds of the rightside electric motor 11R and the left side electric motor 11L to bedifferent from each other, the conveying speeds in the left and right inthe nozzle direction can be different from each other; specifically, byarranging the rotational speed of the right side electric motor 11Rhigher than the rotational speed of the left side electric motor 11L,the conveying speed in the right side in the nozzle array direction canbe made higher than that in the left side, and by arranging therotational speed of the left side electric motor 11L higher than therotational speed of the right side electric motor 11R, the conveyingspeed in the left side in the nozzle array direction can be made higherthan that in the right side.

The first liquid jet heads 2 and the second liquid jet heads 3 include aset of colors, yellow (Y), magenta (M), cyan (C), and black (K) shiftedin the conveying direction of the print medium 1. The liquid jet heads 2and 3 are supplied with liquids from liquid tanks (not shown) of theirrespective colors via liquid supply tubes (not shown). Each of theliquid jet heads 2 and 3 is provided with a plurality of nozzles formedin the nozzle array direction and by emitting the necessary amount ofliquid jet from the respective nozzles simultaneously to the necessarypositions microscopic liquid dots are formed on the print medium 1. Byperforming the process described above by the set of colors, one-passprint can be achieved by making the print medium 1 conveyed by the firstand second conveying sections 4 and 5 pass therethrough once. In otherwords, the area in which the liquid jet heads 2 and 3 are disposedcorresponds to the print area.

As a method of emitting liquid jets from each of the nozzles of theliquid jet heads, an electrostatic method, a piezoelectric method, afilm boiling jet method and so on, can be explained. In theelectrostatic method, when a drive signal is provided to anelectrostatic gap as an actuator, a diaphragm in the cavity is displacedto cause pressure variation in the cavity, and the liquid is emittedfrom the nozzle in accordance with the pressure variation. In thepiezoelectric method, when a drive signal is provided to a piezoelectricelement as an actuator, a diaphragm in the cavity is displaced to causepressure variation in the cavity, and the liquid is emitted from thenozzle in accordance with the pressure variation. In the film boilingjet method, a microscopic heater is provided in the cavity, and isinstantaneously heated to be at a temperature higher than 300° C. tomake the liquid enter the boiling state to generate a bubble, thuscausing a pressure variation and making the liquid be emitted from thenozzle. The present invention can apply to any of the above liquid jetmethods, and among others, the invention is particularly suitable forthe piezoelectric element, capable of adjusting an amount of the liquidjet by controlling the wave height and/or gradient of the increase ordecrease in the voltage of the drive signal.

The liquid jet nozzles of the first liquid jet heads 2 are providedbetween the four first conveying belts 6 of the first conveying section4, and the liquid jet nozzles of the second liquid jet heads 3 areprovided between the four second conveying belts 7 of the secondconveying section 5. Although this is for cleaning each of the liquidjet heads 2 and 3 with a cleaning section described later, the entiresurface is not printed by one-pass printing if either one of the liquidjet heads is used independently. Therefore, the first liquid jet heads 2and the second liquid jet heads 3 are disposed alternately in theconveying direction of the print head 1 in order to compensate for eachother's unprintable areas.

Disposed below the first liquid jet heads 2 is a first cleaning cap 12for cleaning the first liquid jet heads 2, and disposed below the secondliquid jet heads 3 is a second cleaning cap 13 for cleaning the secondliquid jet head 3. Each of the cleaning caps 12 and 13 is formed toallow the cleaning caps to pass between the four first conveying belts 6of the first conveying section 4 and between the four second conveyingbelts 7 of the second conveying section 5. Each of the cleaning caps 12and 13 is composed of a cap body having a rectangular shape with a top,covering the nozzles provided on the lower surface, namely the nozzlesurface of the liquid jet heads 2 and 3, and capable of adhering to thenozzle surface, a liquid absorbing body disposed at the bottom of thecap body, a peristaltic pump connected to the bottom of the cap body,and an elevating device for moving the cap body up and down. The capbody is moved up by the elevating device to be adhered to the nozzlesurface of the liquid jet heads 2 and 3. By causing negative pressure inthe cap body using the peristaltic pump in the present state, the liquidand bubbles are suctioned from the nozzle openings on the nozzle surfaceof the liquid jet heads 2 and 3, thus the cleaning of the liquid jetheads 2 and 3 can be performed. After the cleaning is completed, each ofthe cleaning caps 12 and 13 is moved down.

On the upstream side of the first driven rollers 9R and 9L, there areprovided a pair of gate rollers 14 for adjusting the feed timing of theprint medium 1 from a feeder section 15 and at the same time correctingthe skew of the print medium 1. The skew denotes a rotation of the printmedium 1 with respect to the conveying direction. Further, above thefeeder section 15, there is provided a pickup roller 16 for feeding theprint medium 1. A gate roller motor 17 drives the gate rollers 14.

A belt charging device 19 is disposed below the drive rollers 8R and 8L.The belt charging device 19 is composed of a charging roller 20 having acontact with the first conveying belts 6 and the second conveying belts7 via the drive rollers 8R and 8L, a spring 21 for pressing the chargingroller 20 against the first conveying belts 6 and the second conveyingbelts 7, and a power supply 18 for providing charge to the chargingroller 20. The belt charging device 19 charges the first conveying belts6 and the second conveying belts 7 by providing them with the chargefrom the charging roller 20. Since the belts are generally made of amoderate or high resistivity material or an insulating material, whenthe they are charged by the belt charging device 19, the charge appliedon the surface thereof causes the print medium 1, made similarly of ahigh resistivity material or an insulating material, to achievedielectric polarization, and the print medium 1 can be adhered to thebelt by the electrostatic force caused between the charge generated bythe dielectric polarization and the charge on the surface of the belt.It should be noted that as the belt charging device 19, a corotron forshowering charge can also be used.

Therefore, according to the present printing apparatus, when thesurfaces of the first conveying belts 6 and the second conveying belts 7are charged by the belt charging device 19, the print medium 1 is fedfrom the gate roller 14, and the print medium 1 is pressed against thefirst conveying belts 6 by a sheet pressing roller composed of a spur ora roller (not shown), the print medium 1 is adhered to the surfaces ofthe first conveying belts 6 under the action of dielectric polarization.When the electric motors 11R and 11L drive the drive rollers 8R and 8L,the drive force is transmitted to the first driven rollers 9R and 9L viathe first conveying belts 6.

Thus, the first conveying belts 6 are moved to the downstream side ofthe conveying direction while adhering to the print medium 1, printingis performed by emitting liquid from the nozzles formed on the firstliquid jet heads 2 while moving the print medium 1 below the firstliquid jet heads 2. When the printing by the first liquid jet heads 2 iscomplete, the print medium 1 is moved to the downstream side of theconveying direction to be switched to the second conveying belts 7 ofthe second conveying section 5. As described above, since the secondconveying belts 7 are also provided with the charge on the surfacethereof by the belt charging device 19, the print medium 1 is adhered tothe surfaces of the second conveying belts 7 under the action of thedielectric polarization.

The second conveying belts 7 are moved to the downstream side of theconveying direction, printing is performed by emitting liquid from thenozzles formed on the second liquid jet heads 3 while moving the printmedium 1 below the second liquid jet heads 3. After printing by thesecond liquid jet heads 3 is complete, the print medium 1 is movedfurther to the downstream side of the conveying direction, the printmedium 1 is ejected to a catch tray while separating it from thesurfaces of the second conveying belts 7 by a separating device (notshown).

When cleaning of the first and second liquid ejection heads 2 and 3becomes necessary, as described above, the first and second cleaningcaps 12 and 13 are raised to be adhered to the nozzle surfaces of thefirst and second liquid jet heads 2 and 3, the cleaning is performed byapplying negative pressure to the inside of the caps to suction inkdroplets and bubbles from the nozzles of the first and second liquid jetheads 2 and 3, and then, the first and second cleaning caps 12 and 13are moved down.

Inside the printing apparatus there is provided a control device forcontrolling the apparatus itself. The control device is, as shown inFIG. 2, for controlling the printing apparatus, the feeder device, andso on, based on print data input from a host computer 60, such as apersonal computer or a digital camera, thereby performing the printprocess on the print medium 1. Further, the control device includes aninput interface section 61 for receiving print data input from the hostcomputer 60, a control section 62 formed of a microcomputer forperforming the print process based on the print data input from theinput interface section 61, a gate roller motor driver 63 for drivingthe gate roller motor 17, a pickup roller motor driver 64 for driving apickup roller motor 51 for driving the pickup roller 16, a head driver65 for driving the liquid jet heads 2 and 3, a right side electric motordriver 66R for driving the right side electric motor 11R, a left sideelectric motor driver 66L for driving the left side electric motor 11L,and an interface 67 for converting the output signals of the drivers 63,64, 65, 66R, and 66L into drive signals used in the gate roller motor17, the pickup roller motor 51, the liquid jet heads 2 and 3, the rightside electric motor 11R, and the left side electric motor 11L.

The control section 62 is provided with a central processing unit (CPU)62 a for performing various processes, such as the print process, arandom access memory (RAM) 62 c for temporarily storing the print datainput via the input interface 61 and various kinds of data used inperforming the print process of the print data, and for temporarilydeveloping an application program, such as for the print process, and aread-only memory (ROM) 62 d formed of a nonvolatile semiconductor memoryand for storing the control program executed by the CPU 62 a and so on.When the control section 62 receives the print data (image data) fromthe host computer 60 via the interface section 61, the CPU 62 a performsa predetermined process on the print data to output printing data (drivepulse selection data SI & SP) regarding which nozzle emits the liquidand/or how much liquid is emitted, and further outputs the controlsignals to the respective drivers 63, 64, 65, 66R, and 66L based on theprinting data and the input data from the various sensors. When thecontrol signals are output from the respective drivers 63, 64, 65, 66R,and 66L, the control signals are converted by the interface section 67into the drive signals, the actuators (in the present embodiment, thedrive circuit in the anterior thereof) corresponding to a plurality ofnozzles of the liquid jet heads 2 and 3, the gate roller motor 17, thepickup roller motor 51, the right side electric motor 11R, and the leftside electric motor 11L respectively operate, thus the feeding andconveying the print medium 1, posture control of the print medium 1, andthe print process to the print medium 1 are performed. It should benoted that the elements inside the control section 62 are electricallyconnected to each other via a bus (not shown).

The head driver 65 is provided with a drive waveform generator 70 forforming drive waveform signal WCOM and an oscillator circuit 71 foroutputting a clock signal SCK. The drive waveform generator 70 is, asdescribed in detail below, for generating the drive waveform signalWCOM, which becomes the basis for the drive pulse to the actuator 22,and as shown in FIG. 3. After inputting the clear signal CLER, the drivewaveform generator 70 retrieves the waveform data stored in the waveformdata memory described below and outputs the voltage signal composed ofthe waveform data to form the drive waveform signal WCOM for everypredetermined period ΔT defined by the clock signal CLK. The drivewaveform signal WCOM is power-amplified and converted into the drivepulse to the actuator 22 by the drive circuit composed of a digitalpower amplifier and a low-pass filter described later.

The drive waveform signal WCOM thus generated can be obtained astrapezoidal voltage wave signals with various waveforms shown in FIG. 4by adjusting the waveform data. By power-amplifying this signal in thedrive circuit shown in FIG. 5 and then supplying it to the actuator 22of the liquid jet heads 2 and 3 as the drive pulse, the actuator can bedriven and the liquid jet can be emitted from the nozzle correspondingto the actuator. The drive circuit is configured with for every actuatoras described below, a modulator 24 for performing the pulse widthmodulation on the drive waveform signal WCOM generated by the drivewaveform generator 70, a digital power amplifier 25 for performing thepower amplification on the modulated (PWM) signal, and a low pass filter26 for smoothing the modulated (PWM) signal power-amplified by thedigital power amplifier 25.

The rising portion of the drive waveform signal WCOM or the drive pulsecorresponds to the stage of expanding the capacity of the cavity(pressure chamber) communicating to the nozzle to pull in the liquid (itcan be said that the meniscus is pulled in considering the emissionsurface of the liquid), and the falling portion of the drive signal COMcorresponds to the stage of reducing the capacity of the cavity to pushout the liquid (it can be said that the meniscus is pushed outconsidering the emission surface of the liquid), as a result of pushingout the liquid, the liquid jet is emitted from the nozzle. The series ofwaveform signals from pulling in the liquid to pushing out the liquidaccording to desired output form the drive pulse.

By variously changing the gradient of increase and decrease in voltageand the height of the drive pulse formed of this trapezoidal voltagewave, the pull-in amount and the pull-in speed of the liquid, and thepush-out amount and the push-out speed of the liquid can be changed,therefore, the amount of liquid jet can be changed to obtain a differentsize of liquid dot, and by forming liquid dots with different sizes,finer tone can be achieved. It should be noted that the drive pulseshown in the left end of FIG. 4 is only for pulling in the liquid butnot for pushing out the liquid. This is called a fine vibration, and isused for preventing the nozzle from drying when not emitting the liquidjet.

FIG. 6 shows the overall configuration of the drive circuit separatelyprovided to each of the actuators 22. As described above, since in thepresent embodiment the individual drive waveform signal WCOM to each ofthe actuators 22 is set by the drive waveform generator 70, assumingthat the number of the actuators 22 is N, N drive waveform signalsWCOM(1) through WCOM(N) are output and applied to the N actuators 22 viathe individual drive circuits.

FIG. 7 shows a specific configuration of the modulator 24 of the drivesignal output circuit described above. As the modulator 24 forperforming the pulse width modulating on the drive waveform signal WCOM,a common pulse width modulation (PWM) circuit is used. The modulator 24is composed of a well known triangular wave oscillator 32, and acomparator 31 for comparing the triangular wave output from thetriangular wave oscillator 32 with the drive waveform signal WCOM.According to the modulator 24, as shown in FIG. 8, the modulated (PWM)signal is set to HIGH when the drive waveform signal WCOM is higher thanthe triangular wave, and is set to LOW when the drive waveform signalWCOM is lower than the triangular wave. It should be noted that althoughin the present embodiment a pulse width modulation circuit is used asthe modulator, a pulse density modulation (PDM) circuit can also beused.

The digital power amplifier 25 is configured including a half-bridgedriver stage 33 composed of a MOSFET TrP and TrN for substantiallyamplifying the power, and a gate drive circuit 34 for controlling thegate-source signals GP and GN of the MOSFET TrP and TrN based on themodulated (PWM) signal from the modulator 24, and the half-bridge driverstage 33 is formed by combining the high-side MOSFET TrP and thelow-side MOSFET TrN in a push-pull manner. Assuming that the gate-sourcesignal of the high-side MOSFET TrP is GP, the gate-source signal of thelow-side MOSFET TrN is GN, and the output of the half-bridge driverstage 33 is Va, FIG. 9 shows how these signals vary in accordance withthe modulated (PWM) signal. It should be noted that the voltage valuesVgs of the gate-source signals GP and GN of the respective MOSFET TrPand TrN are assumed to be sufficient to turn on the MOSFET TrP and TrN.

When the modulated (PWM) signal is in the HIGH level, the gate-sourcesignal GP of the high-side MOSFET TrP becomes the HIGH level while thegate-source signal GN of the low-side MOSFET TrN becomes the LOW level,the high-side MOSFET TrP becomes the ON state while the low-side MOSFETTrN becomes the OFF state, and as a result, the output Va of thehalf-bridge driver state 33 becomes the supply voltage VDD. On the otherhand, when the modulated (PWM) signal is in the LOW level, thegate-source signal GP of the high-side MOSFET TrP becomes the LOW levelwhile the gate-source signal GN of the low-side MOSFET TrN becomes theHIGH level, the high-side MOSFET TrP becomes the OFF state while thelow-side MOSFET TrN becomes the ON state, and as a result, the output Vaof the half-bridge driver state 33 becomes zero.

The output Va from the half bridge driver stage 33 of the digital poweramplifier 25 is supplied as a drive signal COM to the selection switch201 via the low pass filter 26. The low pass filter 26 includes acombination of two coils L1 and L2 and two capacitors C1 and C2. The lowpass filter 26 is designed to sufficiently attenuate a high-frequencycomponent, i.e., a amplified digital signal (PWM) component of theoutput Va from the half bridge driver stage 33 of the digital poweramplifier 25 and not to attenuate a drive signal component COM (or drivewaveform component WCOM).

As described above, when the MOSFET TrP and TrN of the digital poweramplifier 25 are driven in a digital manner, since the MOSFET acts as aswitch element, although the current flows in the MOSFET in the ONstate, the drain-source resistance is extremely small and the power lossis small. Further, since no current flows in the MOSFET in the OFF stateno power loss occurs. Therefore, the power loss of the digital poweramplifier 25 is extremely small, a small-sized MOSFET can be used, and acooling unit, such as a heat radiation plate, can be eliminated.Incidentally, the efficiency when the transistor is driven in the linearrange is about 30% while the efficiency of a digital power amplifier ishigher than 90%. Further, since the heat radiation plate for cooling thetransistor is about 60 mm square in size for each transistor, if such aradiation plate can be eliminated, an overwhelming advantage in theactual layout can be obtained.

The configuration and the operation of the drive waveform generator 70will now be explained. The drive waveform generator 70 is configured asshown in FIG. 10, and provided with a shift resistor 111 forsequentially storing the drive pulse selection data SI & SP fordesignating the actuator corresponding to the nozzle from which theliquid jet is emitted, a latch circuit 112 for temporarily storing thedata of the shift register 111 in accordance with a latch signal LAT, adecoder 113 for decoding the data of the latch circuit 112, a waveformdata memory 115 for storing the waveform data corresponding to theactuator 22 as described above, a memory controller 114 for retrievingthe waveform data stored in the waveform data memory 115 and storing itin a cache memory 116 corresponding to the actuator 22 in accordancewith the data decoded by the decoder 113 and the latch signal LAT byperforming the arithmetic process shown in FIG. 12 described below, andan I/O port 117 for outputting the waveform data stored in the cachememory 116 to the modulator 24 of the drive circuit in accordance withthe latch signal LAT and the data decoded by the decoder 113.

The reason why the drive waveform generator 70 outputs the drivewaveform signals WCOM corresponding to the actuators 22 will beexplained. Since the actuator 22, formed of a piezoelectric element orthe like, has a capacitance, if all of the actuators for emitting theliquid jet are connected to one drive pulse in parallel to each other, alow-pass filter is formed of the parasitic inductances, the parasiticcapacitances, and the resistances of the actuators and the wiring of thedrive circuit, therefore, the drive pulses are distorted. Moreover,since the characteristic of the low-pass filter created by thecapacitances of the actuators varies when the number of nozzles foremitting the liquid jet, namely the number of actuators to be driven,varies the state of the distortion of the drive pulse also varies. Everytime the actuator 22, such as a piezoelectric element, is connected tothe low-pass filter, the capacitances are additionally connected inparallel one after another, thus the characteristic of the completelow-pass filter formed by the low-pass filter and the capacitances ofthe actuators can be varied. When the state of the distortion of thedrive pulse varies, the amount of liquid emitted from the nozzle alsovaries, as a matter of course.

Therefore, in the present embodiment, an individual drive circuit isprovided for each of the actuators 22, and an individual drive waveformsignal WCOM is output to each of the drive circuits and, therefore, toeach of the actuators 22. Since the variation in the distortion of thedrive pulse in accordance with the variation in the number of theactuators 22 is eliminated by providing the individual drive circuit toeach of the actuators 22, the variation in the amount of liquid emittedfrom the nozzle can be suppressed even with a common drive waveformsignal WCOM. However, individual differences also exist in the nozzlesand the actuators 22 themselves, and accordingly, even if the drivecircuits of the actuators 22 are provided individually, a variation inthe liquid jet emitted from different nozzles is caused by the commondrive waveform signal WCOM.

In consideration of the individual difference among the nozzles and theactuators 22, in the present embodiment, as shown in FIG. 11A, smallliquid dot waveform data (small ink droplet waveform data, in thedrawing) of the drive waveform signal most appropriate for the drivepulse when forming a small liquid dot, medium liquid dot waveform data(medium ink droplet waveform data, in the drawing) of the drive waveformsignal most appropriate for the drive pulse when forming a medium liquiddot, and large liquid dot waveform data (large ink droplet waveformdata, in the drawing) of the drive waveform signal most appropriate forthe drive pulse when forming a large liquid dot are obtained for Nnozzles and actuators by measurement, and the data is stored into thewaveform data memory 115 corresponding to the address numbers 1 though Min the order of the nozzle number 1 through N.

In this case, the memory controller 114 accesses the address number 2 ofthe waveform data memory 115 in FIG. 11A in accordance with the drivepulse selection data SI & SP when the medium liquid dot is required forthe nozzle number 1, accesses the address number 4 of the waveform datamemory 115 when the small liquid dot is required for the nozzle number2, and stores the waveform data stored therein corresponding to theseaddress numbers in the cache memory 116 corresponding thereto. Thewaveform data stored in all of the cache memories 116 are simultaneouslyoutput from the I/O port 117 as the drive waveform signals WCOM in apredetermined sampling cycle after a predetermined period of time t haselapsed from the latch signal LAT.

It should be noted that in order to decrease the storage capacity of thewaveform data memory 115, similar waveform data to all of the actuators22 of the nozzles shown in FIG. 11A are combined, and storedcorresponding to the addresses by a shape like small ink dropletwaveform data A, medium ink droplet waveform data A, large ink dropletwaveform data A, small ink droplet waveform data B, medium ink dropletwaveform data B, and so on as shown in FIG. 11B. In this case, thememory controller 114 accesses the address number 5 of the waveform datamemory 115 in FIG. 11B in accordance with the drive pulse selection dataSI & SP when the medium liquid dot is required for the nozzle number 1,accesses the address number 1 of the waveform data memory 115 when thesmall liquid dot is required for the nozzle number 2, and stores thewaveform data stored therein corresponding to these address numbers inthe cache memory 116 corresponding thereto. The waveform data stored inall of the cache memories 116 are simultaneously output from the I/Oport 117 as the drive waveform signals WCOM in a predetermined samplingcycle after a predetermined period of time t has elapsed from the latchsignal LAT.

FIG. 12 shows the arithmetic process for retrieving and outputting thewaveform data performed in the memory controller 114 of FIG. 10. In thisarithmetic process, the drive pulse selection data (print data in thedrawing) SI & SP is first received in step S1.

Subsequently, the process proceeds to step S2 to determine whether ornot the latch signal LAT is input, and if the latch signal LAT has beeninput, the process proceeds to step S3, otherwise the process proceedsto step S1.

In step S3, the drive pulse selection data (the print data) SI & SP thusreceived is latched by the latch circuit 112, and further deciphered(decoded in the drawing) by the decoder 113.

Then, the process proceeds to step S4 to start the timer count Tc.

Subsequently, the process proceeds to step S5 to obtain the data (thedecoder signal in the drawing) deciphered by the decoder 113.

Then, the process proceeds to step S6 to designate the address of thewaveform data memory 115 to obtain the waveform data necessary for eachof the actuators.

Then, the process proceeds to step S7 to access the address of thewaveform data memory 115, thus obtaining the waveform data necessary foreach of the actuators.

Subsequently, the process proceeds to step S8 to store the waveform dataobtained in the S7 into the corresponding cache memory 116.

Subsequently, the process proceeds to step S9 to judge whether or notthe timer count Tc has reached the predetermined time period t, and ifthe timer count Tc has reached the predetermined time period t, theprocess proceeds to step S10, otherwise the process enters the standbystate.

In step S10, the waveform data is retrieved from the cache memory 116 inthe sampling cycle, and output from the I/O port 117.

Subsequently, the process proceeds to step S11 to judge whether or notthe transmission of all of the waveform data has been completed, and ifthe transmission of all of the waveform data has been completed, theprocess returns to the main program, otherwise the process proceeds tostep S10.

According to the arithmetic process, as shown in FIG. 13, the waveformdata is output every predetermined sampling time period after thepredetermined time period t has elapsed from the latch signal LAT, thusthe drive waveform signals WCOM are output simultaneously to theactuators 22 of all of the nozzles from which the liquid jets areemitted, and the signals are power-amplified by the respective drivecircuits to be converted into the drive pulses, and are applied to therespective actuators 22. Since only one actuator 22 is connected to onedrive pulse, the drive pulse is never distorted.

As described above, according to the printing apparatus of the presentembodiment, the same number of half-bridge driver stages 33 (eachcomposed of two transistors MOSFET TrP, TrN forming a pair connected ina push-pull manner) as the number of actuators are provided forpower-amplifying the drive waveform signals WCOM as a basis of the drivepulses to the actuators 22. The low-pass filters 26 are provided betweenthe connection points of the pairs of transistors MOSFET TrP, TrN of thehalf-bridge driver stages 33 and the actuators 22, resulting in only oneactuator 22 connected to the drive circuit composed of the half-bridgedriver stage 33 and the low-pass filter 26. Therefore, the waveformdistortion of the drive pulse can be prevented, eliminating and/orpreventing variation in the amount of liquid jetted, thereby making itpossible to perform high quality, fine tone, printing.

Further, since the number of modulators 24 for performing thepulse-modulation of the drive waveform signals WCOM and the number ofgate drive (driving) circuits 34 for driving the half-bridge driverstages 33 (the transistor pairs) based on the pulse-modulated modulationsignal is the same as the number of half-bridge driver stages 33 and areprovided to individually control the half-bridge driver stages 33 inaccordance with the respective drive waveform signals WCOM, thevariation in the amount of liquid jetted among the nozzles can besuppressed and prevented by generating drive waveform signals WCOMcorresponding to the actuators 22 of the drive circuits and the nozzles,thus making it possible to perform high quality, fine tone, printing.

Further, by generating the drive waveform signal WCOM for everycorresponding actuator 22 in accordance with the waveform datacorresponding to the actuator 22 and stored in the waveform data memory115, the variation in the amount of liquid jetted among the nozzles canbe suppressed and prevented, thus making it possible to perform highquality, fine tone, printing.

Further, when the configuration of simultaneously generating the drivewaveform signals WCOM to all of the actuators 22 corresponding to thenozzles from which the liquid jets are emitted with the timing ofemitting the liquid jets from the nozzles is adopted, the shift in theliquid jet emission timing among the nozzles can be prevented, thusmaking it possible to perform high quality, fine tone, printing.

Further, since the modulators 24, the gate drive (driving) circuits 34,the half-bridge driver stages 33 (the transistor pairs), and thelow-pass filters 26 are disposed adjacent to the actuators 22 as anintegrated circuit, the power loss can be reduced to achieve low powerconsumption, and a plurality of liquid jet heads can efficiently bearranged, thus reduction in the size of the printing apparatus becomespossible.

Further, since the transistor pair is connected to every actuator 22,the current flowing through the transistor pair can be reduced, thus itbecomes possible to configure the transistor pair using transistorscapable of operating at higher speed to increase the modulationfrequency to simplify the low-pass filter. For example, the low-passfilter can be composed of a first-order RC filter, or can be composed ofonly a resistor utilizing the capacitance of the actuator, or can becomposed of the resistor components of the wiring and the transistorsand the capacitance component of the actuator without separatelyproviding a low-pass filter.

It should be noted that although in the present embodiment, applying thepresent invention using a line head printing apparatus, the liquid jetapparatus and the printing apparatus according to the present inventioncan also be applied to a multi-pass printing apparatus or any othertypes of printing apparatuses for printing letters or images on a printmedium by emitting liquid jet as a target thereof. Further, each sectionconfiguring the liquid jet apparatus or the printing apparatus of thepresent invention can be replaced with an arbitrary configurationcapable of exerting a similar function, or added with an arbitraryconfiguration.

Further, as a liquid emitted from the liquid jet apparatus of thepresent invention, there is no particular limitation, and liquids(including dispersion liquids such as suspensions or emulsions)containing various kinds of materials as mentioned below can be cited,for example. Specifically, ink containing a filter material of a colorfilter, a light emitting material for forming an EL light emitting layerin an organic electroluminescence (EL) device, a fluorescent materialfor forming a fluorescent substance on an electrode in a field emissiondevice, a fluorescent material for forming a fluorescent substance in aplasma display panel (PDP) device, electrophoretic material for formingan electrophoretic substance in an electrophoretic display device, abank material for forming a bank on a substrate W, various coatingmaterials, a liquid electrode material for forming a electrode, aparticle material for forming a spacer for forming a microscopic cellgap between two substrates, a liquid metal material for forming metalwiring, a lens material for forming a microlens, a resist material, alight diffusion material for forming a light diffusion material, and soon can be cited.

Further, in the present invention, the print medium to be a target ofthe liquid jet emission is not limited to a piece of paper such as arecording sheet, but can be a film, a cloth, a nonwoven cloth, or othermedium, or works such as various substrates such as a glass substrate,or a silicon substrate.

1. A liquid jet apparatus comprising: a plurality of nozzles; anactuator provided for each nozzle and connected to the respectivenozzle; a drive waveform signal generation unit that generates a drivepulse for each actuator; and a drive unit for each actuator for applyingthe drive pulse to the respective actuator, wherein the drive unitincludes: a transistor pair, wherein the transistor pair: has twotransistors connected to each other in a push-pull manner; andpower-amplifies the drive pulse; and a low-pass filter disposed betweenthe transistor pair and the actuator.
 2. The liquid jet apparatusaccording to claim 1, each drive unit further comprising: a modulatorunit for pulse-modulating the drive pulse to produce a modulated signal;and a gate drive unit for driving the transistor pair in accordance withthe modulated signal.
 3. The liquid jet apparatus according to claim 2,further comprising a waveform data memory for storing waveform datacorresponding to the actuators, wherein the drive waveform signalgeneration unit generates the drive pulse for each actuator inaccordance with the corresponding waveform data stored in the waveformdata memory.
 4. The liquid jet apparatus according to claim 3, whereinthe drive waveform signal generation unit provides the drive pulsessimultaneously with the timing of emitting the liquid jet from thenozzles to all of the actuators corresponding to the nozzles from whichthe liquid jet is to be emitted.
 5. The liquid jet apparatus accordingto claim 2, wherein the drive unit is disposed adjacent to the actuatorsas an integrated circuit.
 6. A printing apparatus comprising: aplurality of nozzles for a liquid jet head; an actuator provided foreach of nozzle and connected to the respective nozzle; a drive waveformsignal generation unit that generates a drive pulse for each actuator;and a drive unit for each actuator that applies the drive pulse to therespective actuator, wherein the drive unit includes: a transistor pair,wherein the transistor pair: has two transistors connected to each otherin a push-pull manner, and power-amplifies the drive pulse; and alow-pass filter disposed between the transistor pair and the actuator.7. The printing apparatus according to claim 6, the drive unit furthercomprising: a modulator unit for pulse-modulating the drive pulse toproduce a modulated signal; and a gate drive unit for driving thetransistor pair in accordance with the modulated signal.
 8. The printingapparatus according to claim 7, further comprising a waveform datamemory for storing waveform data corresponding to the actuators, whereinthe drive waveform signal generation unit generates the drive pulse foreach actuator in accordance with the corresponding waveform data storedin the waveform data memory.
 9. The printing apparatus according toclaim 8, wherein the drive waveform signal generation unit provides thedrive pulses simultaneously with the timing of emitting the liquid jetfrom the nozzles to all of the actuators corresponding to the nozzlesfrom which the liquid jet is to be emitted.
 10. The printing apparatusaccording to claim 7, wherein the drive unit is an integrated circuitdisposed adjacent to the actuators.